This can be explained with the following example: The form submission tracking on your website is set up to track events and conversions (key events) on form submission. If a form is submitted, it will be counted as a 'key event' and also as an event.
However, if you decide to resubmit the form because you thought you filled it wrong the first time, for example, the re-submitted form will still be counted as a single 'key event' but the total number of events will be considered as two. This is why 'key events' are sometimes less than actual events.
